Vehicle brake systems typically have a service brake that has service brake apply modes and a parking brake system that has parking brake apply modes. During a service brake apply hydraulic pressure is applied to a piston that moves the piston. In recent systems, during a parking brake apply an electric motor and drive mechanism moves the piston to create the parking brake apply. Once the parking brake apply is complete the motor is turned off. Typically, worm gear or some other threaded member (e.g., lead screw) is located between the piston and the motor, which prevents the piston from back driving the mechanism and motor.
Examples of some brake assemblies may be found in U.S. Pat. Nos. 2,052,846; and 2,823,325 both of which are incorporated by reference herein for all purposes. It would be attractive to have a brake that prevents back drive of a motor when the motor is turned off. What is needed is motor brake that prevents back drive of the drive mechanism when the brake pads are compressed by a drive mechanism such as a high efficiency rotary to linear actuator (e.g., ball screw or ball ramp). What is needed is an electromagnetic motor brake that when activated releases the mechanism and when deactivated defaults to a locked position. It would be attractive to have a motor brake that is brake on when the electromagnet is not powered.